Building products of fiber construction have achieved wide use as decorative ceiling panels in both domestic and commercial buildings. For example, ceiling panels of fiber construction having one surface bearing a decorative design effect such as indentations or fissures and which are painted, usually white, provide an aesthetically pleasing surface and have become widely used as ceiling elements in both residential and commercial structures.
One problem associated with the aforementioned decorative ceiling panels relates to staining of the decorative or face surface of the ceiling panel, especially in high moisture environments. The staining problem is especially acute when decorative ceiling panels are used in the ceiling construction of mobile home structures. For example, mobile type residential or commercial structures have a higher occupancy factor in terms of inhabitants per unit of living space and, as a consequence, a greater volume of moisture vapor is generated in such structures. The increased moisture vapor penetrates through the ceiling structure and condense on colder structural members. Also, mobile type residential or commercial structures are usually constructed to provide a shallow space or plenum between the roof element and the interior ceiling structure thereof. Ordinary air usually occupies the plenum, and the plenum air is normally subjected to rather high temperatures during the daytime hours, followed by much lower temperatures during night-time hours. The wide temperature fluctuations of the plenum air causes considerable condensation of moisture onto the surface of the decorative ceiling panels which faces the plenum area. As a result, moisture accumulated on a panel penetrates through the fibrous body of the ceiling panel and ultimately causes staining of the decorated surface of the ceiling panel due to water soluble, colored materials in the fibrous body of the ceiling panel. The resulting stains discolor the face of the ceiling panel and diminish its otherwise aesthetically pleasing qualities.
Various attempts have been made to apply waterproofing coatings to ceiling panels of fiber construction to minimize absorption of water or water vapor. To illustrate, U.S. Pat. No. 3,204,380 discloses the application of a coating of paraffin wax and low molecular weight polyethylene to the back of an acoustical tile structure to provide a nonstick, waterproof coating.